Testing soil water retention estimation with the MUUF pedotransfer model using data from the southern United States

Soil hydraulic properties have often been estimated rather than measured. S uch estimates are made using pedotransfer functions (PTFs), i.e. regression equations relating soil hydraulic properties to soil basic properties. PTF s were developed from about 18,000 samples from the national soil character ization database that used the clay activity ratio along with texture to ch aracterize the effect of soil minerals on soil hydraulic properties. With t hose PTFs, the Map Unit User File (MUUF) software was developed to use soil series name and textural class of the uppermost soil horizon to estimate s oil water retention. Objectives of this study were: (a) to test the MUUF wi th a database from Southern Plains, and (b) to see whether the MUUF PTFs wi ll be more accurate with actual soil texture data as compared with the soil texture data for the representative pedon of the soil series. The root-mea n-square error (RMSE) of the MUUF estimates of water content at -33 kPa in the uppermost horizon was about 0.04 m(3) m(-3), when only textural class a nd soil names were used. The accuracy did not change when the actual soil t exture was entered in PTFs. In deeper horizons, the RMSE was about 0.065 m, m- when only soil name and textural classes were used. The accuracy improv ed significantly as the actual texture was used instead of the texture deri ved from the representative pedon. Using actual texture halved the RMSE in estimates of water contents at -1500 kPa. The worst estimates were obtained for silt texture. As compared with PTFs found in literature, the MUUF algo rithms provide an average or better accuracy of water retention estimates i n the uppermost soil horizons from the soil series name and textural class. For deep soil horizons, the MUUF pedotransfer algorithms are capable of th e same degree of accuracy provided the information on texture of the deeper soil horizons is available. Published by Elsevier Science B.V.